1. Field of the Invention
The present invention relates to an electronic apparatus, and more particularly, to an electronic apparatus equipped with a backlighting device for backlighting a display and an input device.
2. Description of the Prior Art
Electronic apparatuses such as cellular phone terminals, personal-handy phone system (PHS) terminals, portable information processing devices, electronic databooks, pagers, etc., are typically provided with a display, such as a liquid-crystal display, and an input device having a plurality of keys to display or edit necessary information. Recent electronic apparatuses are also provided with a backlighting device to make the display visible in dark places and to prevent erroneous operations of the input device during input operations. For example, when characters or symbols are input through the keypad in a data input mode, the backlighting device automatically backlights the display and the input device, allowing for easy data input operations even in dark places.
However, a backlighting device also consumes current and continuous backlighting consumes more power than necessary. Thus, various improvements aimed at more efficient power consumption of backlighting have been proposed. There has been widely known, for example, an electronic apparatus having a timer therein to control the backlighting time. More specifically, the electronic apparatus turns on the backlighting device and starts time measurement by the timer when a key input operation is performed. After a lapse of a predetermined time, the backlighting is automatically turned off. Such a configuration can avoid a reduction of the life of a battery caused by long-time lighting induced by the user forgetting to turn it off, etc.
Furthermore, as another conventional example, the ON/OFF control technique for the backlighting has been disclosed in Japanese Patent Laid-Open No. 9-252342. More specifically, a portable telephone with a backlit display is provided with a light-intensity detector that detects surrounding light intensity, a time-of-day clock, and a battery monitor that detects the remaining quantity of a battery. The brightness of the backlit display is determined based on the surrounding light intensity, the time of day, and the remaining quantity of the battery.
However, in the prior art that controls the backlighting time with a timer, the backlighting turns on for a predetermined time with constant brightness. Accordingly, when key is pressed once, the backlighting continues for a while even after the press of the key, thus consuming more power than necessary. Furthermore, when key input operations are performed consecutively, one key operation is followed by another key operation before the lighting time for the first key operation times out. As a result the backlighting remains on continuously, which accelerates the shortening of the life of the battery. This power consumption is particularly noticeable when input operations are carried out for a long time consecutively in data input mode, which is set to make use of functions such as mail transmission/reception and registration of telephone numbers in a telephone directory.
Furthermore, the portable telephone disclosed in the Japanese Patent Laid-Open No. 9-252342 determines the brightness based on the surrounding light intensity, the time of day, and the battery remaining quantity to adjust the brightness of the backlighting. Thus, since the brightness is adjusted irrespective of the screen display status and operating mode, the brightness is set to a level higher than necessary, which leads to an acceleration of power consumption. Moreover, the brightness of the backlighting is generally set to a relatively high level due to the attaching of greater importance to visibility and design factors. But from the standpoint of reducing power consumption it is desirable to reduce the brightness to a necessary minimum level, especially in a battery-powered electronic device.